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fx is a tiny, native coding agent harness written in Zig that focuses on minimalism, performance, and embeddability. Designed to function like a Unix component rather than a heavy IDE, it operates via an approval-gated agent loop and supports custom skills, MCP tools, and subagents.
Version 0.0.6 introduced Gateway defaults using Kimi K3, foreground command timeouts, improved MCP remote server handling, and further binary size optimizations.
As of
- Native Zig binary with <10 microsecond cold start
- Model-agnostic support for local and cloud inference
- Flexible surfaces including CLI, headless JSON mode, and ACP/WASM embedding
- Automatic, permission-gated safety reviews for sensitive actions
- Extensible via Skills, MCP servers, and persistent subagents
Terminal-first developers, CI/CD pipelines, sandboxed agent fleets, and applications requiring a low-footprint, embeddable coding agent.
Critical production pipelines (marked experimental) and users seeking a pre-configured, managed IDE experience.
The software is open-source (Apache-2.0) and free to use; costs are incurred solely through inference providers via Vercel AI Gateway, individual model subscriptions (Codex/Grok), or local compute.
A powerful, ultra-lightweight agent harness that excels in research and programmatic embedding, though it remains in experimental stages and requires manual environment and security configuration.
Is fx free?
Yes - fx is Open Source. The software is open-source (Apache-2.0) and free to use; costs are incurred solely through inference providers via Vercel AI Gateway, individual model subscriptions (Codex/Grok), or local compute.
What is fx best for?
Terminal-first developers, CI/CD pipelines, sandboxed agent fleets, and applications requiring a low-footprint, embeddable coding agent.
Who makes fx?
fx is developed by Vercel Labs. It is listed in the Terminal & CLI Agents category on ai.dosa.dev.
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